This invention relates generally to ultrasonic diagnostic systems which measure the velocity of blood flow using spectral Doppler techniques, and in particular, to automatically adjusting spectral Doppler gain to provide an optimal display for an operator.
Ultrasonic scanners for detecting blood flow based on the Doppler effect are well known. An ultrasonic transducer array transmits ultrasonic waves into an object and receives backscattered ultrasonic echoes. In the measurement of blood flow characteristics, returning ultrasonic waves are compared to a frequency reference to determine the frequency shift imparted to the returning waves by flowing scatterers, such as blood cells. This frequency shift translates into the velocity of the blood flow.
Typical clinical Doppler exams can be time-consuming and involve adjustment of a variety of control keys and switches for setting and adjusting scanning parameters such as sample volume size or sampling gate, flow direction, cursor angle, velocity limits or pulse repetition frequency (PRF), baseline shift and invert, auto max/mean velocity trace, and system gain. Some automation is available, such as for detecting the noise background and signal intensity within the waveform, and for eliminating aliasing by automatically adjusting the PRF. However, there remains a need for automating other Doppler adjustments in order to improve both the speed and reliability of the Doppler exam.
The pulsed or continuous wave (CW) Doppler waveform is computed and displayed in real-time as a spectrum or spectral image of Doppler frequency (or velocity) versus time with the gray-scale intensity (or color) modulated by the spectral power. Each spectral line represents an instantaneous measurement of blood flow within the sampling gate. The data in each spectral line comprises a plurality of frequency bins for different frequency intervals and the signal strength (power) associated with each frequency bin is displayed in a corresponding pixel location on the display. All of the spectral lines taken together form a spectrogram or spectrum.
Each vertical line in the spectrum corresponds to a Doppler frequency spectrum at a given time instant. Positive Doppler frequencies correspond to flow towards the transducer, and negative frequencies correspond to flow away from the transducer, as referenced by a baseline at frequency equal to zero.
Typically, the operator has to adjust system parameters, such as the gain, to adjust the spectrum which is displayed. For example, the signal component of the spectrum may be small and thus difficult to distinguish from the noise component. Alternatively, the signal component may be very high, causing the monitor to saturate and not display the full range of data. In both cases, the system needs to be adjusted manually by the operator. This can be time consuming and can lead to error and/or difficulty in diagnosis if the system parameters are not set properly.
Therefore, a need exists for automatically adjusting system parameters of the ultrasound system during spectral Doppler imaging so that the flow signal and noise background are displayed at optimal brightness levels. Certain embodiments of the present invention are intended to meet these needs and other objectives that will become apparent from the description and drawings set forth below.